Process for producing methylenebis(cyclohexylamine)

Abstract

The present invention provides a process for producing methylenebis(cyclohexylamine), comprising the steps of 1) catalytically hydrogenating MDA, 2) removing the catalyst and 3) subsequently distilling the product of the hydrogenation, in which at least one dividing-wall column is used in step 3). Exposure to high temperature and residence time of the product is reduced and problems due to crystallization do not occur. The methylenebis(cyclohexylamine) isomer ratio also may remain largely constant during the distillation.

1 . A process for producing methylenebis(cyclohexylamine), comprising the steps of
 1. catalytically hydrogenating MDA,   2. removing the catalyst and   3. subsequently distilling the product of the hydrogenation,   
       wherein at least one dividing-wall column is employed in the distillation in step 3). 
     
     
         2 . The process according to  claim 1 , 
       wherein;
 a supported catalyst is used as catalyst during said catalytically hydrogenating MDA, said supported catalyst contains, an active metal in an amount of 0.01% to 20% by weight based on the supported catalyst, and wherein the active metal is ruthenium alone or ruthenium and at least one metal of subgroups I, VII or VIII of the periodic table of the elements. 
 
     
     
         3 . The process according to  claim 1 ,
 wherein the MDA comprises at least 70% by weight of 4,4′-diaminodiphenylmethane and 0.01% to 2% by weight of N-methyl compounds, in each case based on the total mass of compounds having aromatic rings.   
     
     
         4 . The process according to  claim 1 ,
 wherein the distillation of the hydrogenation product in step 3) is carried out exclusively with a dividing-wall column.   
     
     
         5 . The process according to  claim 1 ,
 wherein the dividing wall of the at least one dividing-wall column is continuously present at a height of 15 to 80% of the dividing-wall column, measured from the lower end.   
     
     
         6 . The process according to  claim 1 ,
 wherein the dividing wall of the at least one dividing-wall column has an offset of 0 to 30% of the diameter from the middle towards the sidestream region or inflow region.   
     
     
         7 . The Process according to  claim 1 ,
 wherein the dividing wall of the at least one dividing-wall column is designed as an asymmetric dividing wall.   
     
     
         8 . The process according to  claim 1 , 
       wherein the distillation with at least one dividing-wall column in step 3) is operated such that:
 a) the inflow is located at the height of at least a portion of the dividing wall; 
 b) the sidestream takeoff for drawing off purified methylenebis(cyclohexylamine) is located at the height of at least a portion of the dividing wall, on the other side of the dividing wall from the inflow; 
 c) the distillate is withdrawn at the top of the dividing-wall column and partly discharged and partly returned to the dividing-wall column and 
 d) the bottoms located at the base of the dividing-wall column is discharged. 
 
     
     
         9 . The process according to  claim 8 , 
       wherein the distillate is withdrawn in step c) such that:
 the distillate is withdrawn at the top of the dividing-wall column, 
 it undergoes at least partial condensation in a connected condenser, 
 and at least a portion of the condensate is returned to the top region of the dividing-wall column, and a low boilers stream possibly still present in volatile form downstream of the condenser is discharged together with non-returned condensate. 
 
     
     
         10 . The process according to  claim 1 , wherein the inflow of the at least one dividing-wall column is present at a height of 25 to 66% of the height of the column, measured from the lower end. 
     
     
         11 . The process according to  claim 1 , wherein the at least one dividing-wall column has a number of theoretical plates of from 10 to 90. 
     
     
         12 . The process according to  claim 1 , wherein the at least one dividing-wall column is operated at a bottoms temperature of from 190 to 300° C. 
     
     
         13 . The process according to  claim 1 , wherein the liquid load below the sidestream takeoff and above the bottoms and above the lower end of the dividing wall is less than or equal to 1.5 m 3 /(m 2 h). 
     
     
         14 . Process according to  claim 1 , wherein the sidestream takeoff of the at least one dividing-wall column is located at a height of 30 to 60% of the column, measured from the lower end. 
     
     
         15 . Process according to  claim 1 , wherein the packing beds of the at least one dividing-wall column are 2 to 7 metres in height.